The present invention relates to video display controller systems which are typically employed in small computer systems, terminals and word processors. This invention relates to a manner for reducing data processing overhead and increasing the rate of data transfer pertaining to video characters having associated video attributes.
In the prior art a small computer, terminal or word processing system employs a read/write memory which determines the individual alphanumeric characters displayed upon a video display screen. Typically in such a prior art system, a particular memory location stores a character code corresponding to the alphanumeric character to be displayed at a corresponding location on the video display screen. By changing the contents of a particular memory location, the alphanumeric character displayed at the corresponding position on the video display screen may be changed.
Prior art systems also enable a particular character appearing on the video display screen to have one or more video attributes. These video attributes are employed for special emphasis or visual attention. These video attributes may include various character intensities, character colors, character enable or disable, reverse video, underline and blinking. When a character is enabled it has a foreground/background pattern indicative of the character. When a character is disabled, it is displayed as all background. In reverse video, the foreground and background are reversed. That is, the background is illuminated and the foreground is dark. In an underline mode, the displayed character includes an underline. In a blinking mode, the character remains the same but is periodically turned on and off. In accordance with the prior art, a single character may include more than one of these video attributes, such as a character may be in reverse video or blinking or underlined at the same time.
In accordance with the prior art, a video attribute is stored corresponding to each stored character code for the alphanumeric characters to be shown on the video display screen. This video attribute code carries information concerning the attributes of this particular character which is employed to generate the video signal. In prior art systems, this video character code is read or written at the same time the corresponding character code is read or written. Thus, in order to transfer the data corresponding to an entire screen of alphanumeric text having the same video attributes, it would be necessary to respecify the video attributes each time that an alphanumeric character code is written into the memory.